Originally published: 2004
This is a brilliant launching device – simply due to the sound of the boom when fired! It doesn’t have much of a range when compared to the potato cannons but it does manage to launch a tennis ball about a hundred feet into the air. It also doesn’t have much of a service life as the recoil of firing crumples the bottom-most cans which then have to be replaced in the field, but, it is great fun! The following content is from the original project page.
5 baked bean tins with stacking ridges on base of tins and standard top
1 to 3 baked bean tins with a standard top and base (no stacking ridges)
5mm Ø drill bit and drill
Extended BBQ Lighter
A few bricks and/or something to hold the mortar in firing position
Construction of the mortar
The first problem was to find some stackable baked bean tins and some that did not stack. The photo below on the left is the base of a ridged based tin (one that stacks) and the photo below on the right is of a standard tin with the base cut out (one that does not stack).
I made baffles/holes in four out of the five ridge based tins by cutting out a circle in the bases using a Stanley knife. The hole in each of the bases is about 25mm in diameter. The baffles help to keep the mortar rigid and can improve the overall combustion of the propellant.
I then cut the top and bottom off the standard baked bean tins using a tin opener. These tins are then used for extending the ‘barrel’ part of the mortar. With the remaining ridge based tin I drilled a 5mm Ø hole on its side about 25mm away from the base of the tin.
The diagram below shows how the tins should be stacked (the ‘barrel’ part of the mortar can have any number of extra cans added which is a bit of trial and error but does change the performance of the mortar significantly). I joined each tin together simply using a couple of layers of duct tape.
Last of all I modified the tennis ball using duck tape. To keep the ball spherical, I wrapped the duck tape round in an “X” shape first, and then in a “+” shape. I kept adding layers until the ball fitted smoothly yet snugly down the top section of the mortar.
To use the mortar stack up some sturdy bricks that can support the mortar well. Place a modified tennis ball down the mortar and spray a very small amount of propellant through the firing hole (or about a teaspoon of lighter fluid). Place the mortar securely and position yourself next to the firing hole and using an extended lighter ignite a flame at the firing hole to ignite the propellant inside – BOOM!